Recently, a technology related to a non-contact information storage medium (hereinafter referred to as “non-contact card”) such as an identification (ID) card or radio frequency (RF) tag has been rapidly developed. The non-contact card includes an antenna pattern formed on a resin substrate or the like and a semiconductor integrated circuit (IC) chip (hereinafter referred to as “IC chip”) connected to an antenna terminal disposed at one end of the antenna pattern.
Non-contact cards using a band of 13.56 MHz are presently used as a commuter pass or a prepaid card by a railroad company.
Such non-contact cards have been reduced in size and cost by technology development, and have been recently used in further various fields. For instance, they are used for constructing a uniform management system for production management or distribution management of articles or for managing the security of small articles or books. For spreading the use of the non-contact cards, further convenience enhancement and cost reduction of them are required. For instance, non-contact cards having flexibility are required, communication distance is required to be increased, and variation in communication distance is required to be decreased.
A structure for increasing the communication distance is disclosed in Japanese Patent Unexamined Publication No. 2002-298106 (hereinafter referred to as “Patent document 1”). This document shows a non-contact card having the following elements:                an IC chip for storing data;        an antenna for transmitting and receiving the data using electromagnetic wave in a non-contact manner; and        a reflecting means that is faced to the antenna and reflects the electromagnetic wave toward the antenna.        
The structure in Patent document 1 has the reflecting means, and hence can increase the communication distance without requiring a battery. This structure can keep the data reading/writing state constant regardless of material disposed on the rear surface.
For suppressing the variation in communication distance caused by characteristic variation of the base material when a microwave band is used, Japanese Patent Unexamined Publication No. 2005-71179 (hereinafter referred to as “Patent document 2”) discloses a non-contact card. The non-contact card of Patent document 2 has the following elements:                a base material made of paper;        a communicating means that is disposed in the base material, and transmits and receives data using electromagnetic wave that is supplied from an external reader/writer and is in a range from an ultrahigh frequency (UHF) band to a microwave band that is;        an IC chip having a storing means for storing the data writably or only readably;        an antenna unit made of an electric conductor connected to the IC chip; and        a covering layer that is disposed between the base material and the antenna unit and is made of material that has water resistance and hardly varying dielectric constant.        
For achieving the miniaturization while securing the communication distance, Japanese Patent Unexamined Publication No. 2000-295024 (hereinafter referred to as “Patent document 3”) discloses a non-contact tag having the following structure. The non-contact tag has an antenna substrate including the following elements:                a dielectric substrate having a predetermined dielectric constant; and        flat antenna coils separately formed using an antenna conductor on both sides of the dielectric substrate so that the current flows in the same direction.        
In the non-contact card of Patent document 1, however, the interval between the antenna and the reflecting means depends on the wavelength of the electromagnetic wave used for reading and writing data. Therefore, this interval is required to be set at a predetermined interval in order to increase the communication distance. When the wavelength is 2.45 GHz, for example, the interval is required to be at least 7.7 mm. In this method, the communication distance can be increased, but it is difficult to achieve a thin non-contact card.
Patent document 2 shows that the drift of the resonance frequency of the antenna unit can be reduced by suppressing the variation in dielectric constant of the paper-made base material in the non-contact card thereof. However, Patent document 2 does not show or suggest that the communication distance depends on the mounting state of the IC chip.
In the non-contact tag of Patent document 3, a resonance circuit is formed of a stray capacitance between the antenna coils formed on both surfaces of the dielectric substrate and an inductance of the antenna coils. Thus, the opening is enlarged while the non-contact tag is miniaturized, and the communication distance is improved. However, Patent document 3 does not show or suggest that the communication distance depends on the mounting state of the IC chip, similarly to Patent document 2. This structure is not so effective when ultra-short wave of about 956 MHz or microwave of about 2.45 GHz is used.
Generally, when thermoplastic resin base material such as polyethylene terephthalate (PET) resin is used as the base material of the non-contact card or the like, the resin substrate can deform depending on the condition of heating temperature, pressurizing load, or the like in connecting the IC chip to the antenna terminal of the antenna pattern. The antenna pattern including the antenna terminal is recessed by the deformation, and hence the interval between the circuit forming surface of the IC chip and the antenna terminal can become extremely short.
The inventors newly find that the communication distance significantly varies when the interval between the circuit forming surface of the IC chip and the antenna terminal decreases.